Abstract
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•The NiO-NiPi and NiP/NiO-NiPi with crystalline/amorphous interfaces were constructed.•The NiO-NiPi and NiP/NiO-NiPi display superior UOR and HER activity, respectively.•Different activities were related to the tunable interface structure and composition.
The intrinsically sluggish reaction dynamics of urea electrolysis at large current densities promote one to develop highly efficient catalysts so as to enable widely application of this meaningful catalytic model. In response, the Ni-P-O-based micro-nanostructures with rich crystalline/amorphous interface are rationally constructed by a facile electrodeposition strategy. A nickle oxide/phosphate (NiO-NiPi) synthesized under −1.2 V for 1 min displays prominent activity for catalyzing the anodic urea oxidation reaction (UOR), whereas a nickel phosphide/NiO-NiPi generated under −1.1 V for 20 min (named as NiP/NiO-NiPi) possesses a faster cathodic hydrogen evolution reaction (HER) dynamics. Such tunable catalytic activities of the NiO-NiPi and NiP/NiO-NiPi may be correlated with their different interface structure and composition, which could accelerate the charge and electron transfer as well as increase active sites density for facilitating the absorption of urea and water. Impressively, the whole assembled cell using the developed NiO-NiPi//NiP/NiO-NiPi couple could deliver as high as 250 mA cm−2 at an ultra-low potential of 1.67 V, 345 mV less than that of the pure water electrolysis, which hence makes an important step forward in obtaining massive energy-saving hydrogen by urea electrolysis at large current density.